AWB Limited faces a watershed in its 69-year history this week if growers vote to change the company's constitution.

For nearly 40 years, the wheat marketer has had a grain grower as its chairman but that may be about to change.

If the vote on constitutional change is passed at the resumed general meeting of AWB today, control of the company will eventually fall into the hands of the five independent directors on the board.

Those directors - Peter Polson, John Howarth, John Schmoll, Fred Grimwade and managing director Gordon Davis - will be responsible for deciding who fills the two grower positions on the board and who will be the new chairman.

And the odds-on favourite is Mr Polson, who was elected deputy chairman earlier this year.

The last non-grower who was chairman of AWB or its predecessor, the Australian Wheat Board, was Sir Allan Callaghan, who served from 1965 to 1971.

When he was succeeded by NSW grower Jack Cass in 1971, that began a long succession of grain growers heading the organisation: Sir Leslie Price, Clinton Condon, Trevor Flugge and current chairman Brendan Stewart.

If, as expected, AWB achieves the required 75 per cent vote at today's ballot, another meeting must be called within 21 days and held within another two months to pass the new constitution.

At that meeting, the vote on the new constitution must be passed with a 75 per cent majority, but that will not be an obstacle, with institutional investors backing the ballot.

The meeting will also see A-class directors resigning, if they had not already done so.